My car has an odd 2-1 Downshift clunk, more like a thud, it's hard enough that the low trac light will pop on for a few, even in dry weather. I'm not sure what it could be. It's just done it since the transmission went in. What are some possible causes I can check without just throwing parts at it till something sticks?

Car does have a UMI tq arm and relocation crossmember, but the clunk was there with the stock stuff in there too, it's just more noticeable now, to the point it's actually annoying.

 

At what MPH does this 2-1 downshift clunk happen. Are you talking about a forced 2-1 from 30MPH or a 2-1 coast-down? Most coast-down 2-1 downshifts are scheduled for under 3 MPH.

 

Did they install the HD 2-3 shift valve?

 

That's a good question, I've not paid enough attention to speed to realize where it does it. But I believe I'm going over 3mph when it happens, I'll go for a drive later and double check and get back to you on that.

As for the 2-3 Shift valves, it's a Performabuilt Level 2 unit, Not sure what all they have done besides what's listed in the description of it. Nothing about a HD 2-3 valve, but it very well could have one.

 

Does it do it in all gears? Does it just do it in manual 3rd?

 

dont know if the TG springs were used in the 1-2....but they have been known to break

 

just need some more details on when it happens and under what conditions to decide what is really going on at that specific time.

Because it is a @performabuilt unit maybe we can get him to chime in on this one...

 

I do not believe that Performabuilt uses any TransGo 2nd Accumulator Piston Springs...

 

What are the Torque Converter Specs?

Is this on a Manual Down-Shift (Gear Selector moved into D1 Position)?

 

It's a Yank SS3600, and it just happens while in drive, doesn't happen every time, but it's 50/50 when coming to stop or slowing down if it's going to do it or not.

 

Intermittent issues are the worst to deal with!! Next time it does it think about the previous 5 minutes drive.
What had you just done and can it be duplicated?
Did you full throttle it and coast back down to a stop light?
Is it only after a full warm up and a long highway drive?
Is it only after having Manual shifting it?
I think you see where I'm going.
Might want to put a pressure gauge on it and see what pressure it has when it happens. Could be that pressure is not coming back to under 100psi as you coast down to a stop.

 

No experience to note with a built trans but my stock 4L60 unit in my 98 "jerks/lurches" slightly on the 2-1 downshift right before a complete stop is completed. It did this with the stock converter as well as a PTC 3600 unit. It has done this with the two different sets of new u-joints. Oddly, immediately after changing the joints both times it went away for a day or 2..

The good news... it has done this for about 30,000 miles including some beatings and it has never gotten worse and I don't even notice it anymore.... lol. I've chalked it up to some drive train slack and considered it harmless.

 

Yeah I've beat on mine too and I'm not worried about transmission failure, just an annoyance. I think I actually tracked mine down to the motor mounts. They're completely shot, and as I paid more and more attention to it, the clunk comes from under your feet.

 

I feel Your bump or thud going from second to first gear at 3 mph with an original A4 and a small stall. I believe it's a characteristic of the transmission but it's quite annoying when you're about to come to a stop while coasting. I'm hoping I can raise or lower the shift point so it will do it when I'm not ready to come to a stop? I don't have any lights coming on but that could be because my line pressure is lower or it's stock and not a built transmission? I'm hoping somebody here smarter than me can help?

 

If it's a PB Unit it likely has what is called the "full time overrun mod" I came up with it years ago, It basically keep the overrun clutch on in all gears but 4th, Its greatly improves sprag durability in fact not a single sprag break after is was added. What you are feeling is the 3-2 downshift and since they use a pancake style servo and wide band it may be rather aggressive (pancake style meaning no size differential front to rear of second servo) nothing wrong with that but much like the superior servo will tend to be clunky.
The Mod itself in fact gives you a much stronger transmission but in some cars and trucks depending on gearing and tune setting can be a little annoying but then performance trans are generally not built with comfort as a high priority..
I had stated since I am no longer at the company I would not do tech support but there is nothing wrong with the trans its part of the build.
Things you can do to make it more tolerable/
1-max out the duty cycle of the 3-2 solenoid
2- Lower the speed at which the coast 3-2 downshift happens but not lower than the 2-1 unless you lower it too.
3- Make sure the line drops to idle line when coasting should be 60 to 80 psi. This would have to be verified with a gage and ajusted in tune.
4-Make sure converter is unlocking during coast if not this will amplify the feeling several times over.

Otherwise, it is the nature of the build and I use it in all mine also its a major reason these units went from being limited to 800 or so max RWHP to 1000 plus with the right hard parts.

I do not know who came up with it first but have learned that several others have but using different methods than my own but it has become a standard in high power handling units for many. And is necessary if you want the sprag to long term stand up to the abuse of high powered car and trucks in performance applications.
Asking a High performance transmission to feel and act like a stock one and survive is simply not something that can be done.
NOTE YOU CAN FIND MORE INDEPTH DISCUSSION OF THE MOD FROM MYSELF AND OTHERS HERE https://ls1tech.com/forums/automatic...tch-4l60e.html